Heterologous prime-boost with mRNA-1273 stimulates persistent neutralising antibodies in BBIBP-CorV-vaccinated individuals

•This prospective study followed a cohort of BBIBP-CorV-vaccinated individuals.•Heterologous mRNA-based booster elevated NAb titre compared to homologous BBIBP-CorV.•NAb waning observed within 6 months following heterologous vaccination with BNT162b2.•NAb persist up to 9 months post-heterologous mRNA-1273 booster or COVID-19 infection. BBIBP-CorV inactivated vaccine is one of the most prevalent vaccines globally, but immune responses are far less studied than novel COVID-19 vaccine platforms. Longitudinal studies on BBIBP-CorV with homologous and heterologous booster doses are limited. This study follows a subset of participants from a national study comparing the immunogenicity of COVID-19 vaccines and levels of SARS-CoV-2 neutralising antibody (NAb). Homologous and heterologous booster dose significantly increased NAb levels in BBIBP-CorV-vaccinated individuals. Similar NAb levels were observed 1 month following BNT162b2 or mRNA-1273 booster. Interestingly, NAb persisted following mRNA-1273 booster (n = 95), but waned significantly at 6 and 9 months following BNT162b2 booster (n = 50; P > 0.001). The persistence of NAb was also observed following breakthrough infection. This study provides evidence that not all mRNA vaccines are equal in the longer term and should provide valuable information for policy makers planning booster programmes for BBIBP-CorV vaccinated populations.